EP2601416B1 - Pressure medium system, in particular hydraulic system - Google Patents

Description

The invention relates to a pressure medium system, in particular a hydraulic system of a clamping device for the mechanical clamping of workpieces or workpiece holders, such as workpiece pallets.

Such tensioning devices with a hydraulic system are for example out DE 31 36 177 A1 known and include a hydraulic pump, a pressure sensor and a pressure relief valve and a control unit.

The hydraulic pump generates the hydraulic pressure required for operating the tensioning device, wherein the hydraulic pump can be driven, for example, by an electric motor.

The pressure relief valve is arranged between the hydraulic pump and the hydraulic consumer of the tensioning device and returns the hydraulic oil when a predetermined maximum value is exceeded in a hydraulic oil tank to limit the hydraulic pressure to the maximum permitted value.

This pressure limitation may be required, for example, if the hydraulic pump delivers a larger volume flow due to a disturbance than is required to maintain a predetermined desired value.

In addition, this pressure limitation may also be required if the hydraulic oil trapped in the hydraulic system expands due to heating, which is associated with a corresponding increase in pressure.

The control unit measures the hydraulic pressure generated by the hydraulic pump by means of the pressure sensor and turns on the hydraulic pump when the hydraulic pressure falls below a predetermined minimum value (cut-in pressure). In the subsequent pressure build-up, the control unit continuously measures the current hydraulic pressure by means of the pressure sensor and switches off the hydraulic pump when the hydraulic pressure measured by the pressure sensor exceeds the predetermined desired value (switch-off pressure). In this way, the hydraulic pressure is maintained in the operation of the clamping system between the minimum value and the desired value.

The FIGS. 5A to 5D show for such a conventional hydraulic system the time profile of the hydraulic pressure ( FIG. 5A ), the on or off state of the hydraulic pump ( FIG. 5B ), the on or off state of the consumer ( FIG. 5C ) and the on or off state of the pressure relief valve ( FIG. 5D ).

This known hydraulic system has several disadvantages, which will be briefly described below.

On the one hand, part of the volume flow conveyed by the hydraulic pump has to be discharged via the pressure limiting valve when the hydraulic pressure exceeds the predetermined desired value. However, this pressure limitation is associated with a corresponding power loss of the pressure relief valve.

On the other hand, the hydraulic pump is usually operated at a high hydraulic pressure near the target value, which is associated with a correspondingly high load on the hydraulic pump and with a correspondingly high energy consumption.

Furthermore, there is the problem that the hydraulic pump must be turned on again when the hydraulic pressure has dropped below a predetermined minimum pressure. The problem here is the fact that this so-called downstream switching of the hydraulic pump does not immediately lead to a pressure increase, which has different causes. On the one hand, the motor relay of the hydraulic pump to a certain dead time, whereby the start of the hydraulic pump is delayed. In addition, due to its inertia, the hydraulic pump requires a certain start-up time. On the other hand, however, also the hydraulic pressure in the hydraulic system has a time constant and increases linearly after the start of the hydraulic pump. This time delay may cause the downstream of the hydraulic pump to fall below the predetermined minimum pressure.

Out DE 199 59 706 A1 and DE 10 2005 060 321 A1 Pressure fluid systems for a motor vehicle brake system are known, which also occurs the phenomenon that a hydraulic pump does not stop immediately when you turn off, but has a wake. The possible increase in pressure during this overrun when switching off, however, is compensated in these documents by the fact that the control times for downstream valves are modified accordingly. Here, therefore, the pressure increase during the wake is not prevented, but compensated by appropriate control measures.

It should also be noted from the prior art from other technical fields DE 20 2008 011 507 U1 . DE 697 15 709 T2 and DE 197 13 576 A1 ,

Finally, the state of the art should be pointed out DE 10 2005 002 443 A1 . US 2004/0098984 A1 and US 005 829 335 A , However, these documents disclose only a conventional one Control of a pump by, for example, the delivery rate of the pump is varied by driving the pump with an adjustable duty cycle. This is therefore a continuous control in contrast to a switching on or switching off the pump, as provided in the context of the invention.

The invention is therefore based on the object to provide a correspondingly improved hydraulic system that avoids these disadvantages as much as possible.

The invention is based on the technical realization that the fluid pump (for example hydraulic pump) still has an inertia-related overrun even after its drive has been switched off, so that the fluid pressure (for example hydraulic pressure) rises somewhat even after the fluid pump has been switched off during the overrun of the fluid pump.

The invention therefore provides that the fluid pump is already switched off during pressure build-up before the fluid pressure has reached the predetermined desired value. During the subsequent overrun of the fluid pump, the fluid pressure then still rises from the switch-off pressure with a specific follow-up pressure increase in the direction of the predetermined desired value. The invention thus utilizes the kinetic energy of the fluid pump, the drive of the fluid pump and / or the fluid column conveyed by the fluid pump.

On the one hand, this offers the advantage that the fluid pump is less often operated at high fluid pressures near the target value, whereby the fluid pump is spared and consumes less drive energy.

On the other hand, however, the invention also offers the advantage that less fluid (for example hydraulic oil) has to be removed via the pressure-limiting valve, whereby the pressure limiting valve is spared and less power loss occurs.

In a preferred embodiment of the invention, the cut-off pressure is so dimensioned that the pressure difference between the predetermined desired value and the cut-off pressure is smaller than the caster pressure increase. This means that the fluid pressure after switching off the fluid pump at least still rises up to the predetermined desired value. The caster pressure increase should therefore preferably be sufficiently large be to bridge the pressure difference between the cut-off pressure and the target value.

It should be noted that the pressure increase during the wake of the fluid pump asymptotic runs to a final value, so that the pressure increase in the upper pressure range to the end value takes place behind slower and slower. However, it is usually desirable that the predetermined target value of the fluid pressure during the caster set as quickly as possible. Preferably, the cut-off pressure is therefore such that the caster pressure rise exceeds the pressure difference between the cut-off pressure and the predetermined target value by at least 1%, 2%, 5%, 10%, 20%, 50%, 100% or 200% , This offers the advantage that, to bridge the pressure difference between the cut-off pressure and the predetermined target value, the relatively steep initial pressure increase during the overrun is utilized, so that the predetermined setpoint value is established relatively quickly after the fluid pump is switched off.

On the other hand, it is not necessary that the fluid pressure after the shutdown of the fluid pump during the caster even further increases as to the desired target value. The cut-off pressure is therefore preferably such that the lag pressure increase exceeds the pressure difference between the cut-off pressure and the predetermined target value by at most 200%, 100%, 50%, 20%, 10%, 5%, 2% or 1% , This offers the advantage that during the wake of the fluid pump only little excess fluid is obtained, which then has to be removed via the pressure relief valve.

The above percentages are possible when using certain factors in the calculation. However, the invention is not fixed to fixed values. Depending on the stability and characteristics of the hydraulic system There are different values. Preferably, however, the smallest possible value is used within the scope of the invention. This depends on the quality of the calculation, the constancy of the parameters of the hydraulic system and in particular on the rigidity of the system, the reaction rate of the controller and the drive. Desirable values are below 5%.

In the preferred embodiment of the invention, the shutdown and / or the connection of the fluid pump or the drive of the fluid pump is pressure-controlled. This means that the control unit measures the fluid pressure by means of the pressure sensor. The control unit switches off the fluid pump during pressure build-up when the measured fluid pressure exceeds the predetermined cut-off pressure. In addition, the control unit can turn on the fluid pump again when the measured fluid pressure falls below the predetermined switch-on pressure.

When determining the cut-off pressure, it must be taken into account that the caster pressure rise depends not only on the inertia of the fluid pump and its drive, but also on the currently delivered and discharged flow rate. For example, if a large flow rate flows through the consumer, the caster pressure increase is very low. In determining the cut-off pressure, therefore, the current outflow of the fluid pump is preferably taken into account.

One way to determine the current flow rate of the fluid pump is to measure the pump speed of the fluid pump or derived from the engine control, the flow can then be derived at least approximately from the pump speed.

Another possibility for determining the current flow rate of the fluid pump is the measurement by means of a volume flow sensor.

On the other hand, another possibility provides that the flow rate of the fluid pump is assumed to be known.

The inertia of the system of fluid pump and its drive is reflected in operation in the time pressure change during pressure build-up, i. in the first time derivative of the fluid pressure. Thus, a rapid rise in pressure during pressure build-up points to a correspondingly high inertia and a high after-run pressure increase. Preferably, therefore, the temporal pressure change is measured during pressure build-up and taken into account as a measure of the inertia of the fluid pump.

It should also be mentioned that the cut-off pressure during operation of the pressure medium system according to the invention is preferably adapted dynamically to the current operating state. This means that the cut-off pressure is continuously adjusted to the current operating condition (e.g., speed, fluid pressure, pressure rise, etc.).

• Während des Nachlaufs soll der Fluiddruck auf jeden Fall bis auf den vorgegebenen Soll-Wert ansteigen.
• Nach dem Abschalten der Fluidpumpe soll sich der vorgegebene Soll-Wert für den Fluiddruck möglichst schnell einstellen.
• Während des Nachlaufs soll möglichst wenig überschüssiges Fluid-gefördert werden, das zum Erreichen des Soll-Werts nicht erforderlich ist und über das Druckbegrenzungsventil abgeführt werden muss.

In the case of this dynamic adjustment of the switch-off pressure, the following boundary conditions or optimization targets are preferably taken into account:

• During the overrun, the fluid pressure should in any case rise to the specified target value.
• After switching off the fluid pump, the predetermined target value for the fluid pressure should set as quickly as possible.
• During the overrun, as little excess fluid as possible should be pumped, which is not required to reach the setpoint value and has to be dissipated via the pressure relief valve.

mit:

P_AUS:

Abschaltdruck.

P_SOLL:

Soll-Wert für den Fluiddruck.

K1:

Geräteabhängige Konstante, die die Trägheit von Fluidpumpe und Antriebsmotor wiedergibt.

K2:

Geräteabhängige Konstante, die Tot- und Verzögerungszeiten von Pumpe, Motor und Steuereinheit wiedergibt.

P_IST:

Aktueller Fluiddruck.

dP_IST/dt:

Zeitlicher Druckanstieg.

Q:

Förderstrom der Fluidpumpe.

In the preferred embodiment of the invention, the cut-off pressure is therefore calculated according to the following formula and continuously adapted during operation: $${\mathrm{P}}_{\mathrm{OUT}}={\mathrm{P}}_{\mathrm{SHOULD}}-\left(\mathrm{K}\mathrm{1}/{\mathrm{P}}_{\mathrm{SHOULD}}+\mathrm{K}\mathrm{2}\right)\cdot {\mathrm{dP}}_{\mathrm{IS}}/\mathrm{dt}\cdot \mathrm{1}/\mathrm{Q}$$

With:

P _OFF :

Cut-off.

P _SOLL :

Target value for the fluid pressure.

K1:

Device-dependent constant representing the inertia of fluid pump and drive motor.

K2:

Device-dependent constant representing dead and delay times of pump, motor and control unit.

P _IS:

Current fluid pressure.

dP _ist / dt:

Time pressure increase.

Q:

Flow of the fluid pump.

However, the invention is not limited to the above-mentioned formula with regard to the calculation of the switch-off pressure, but in principle can also be implemented with other formulas for calculating the switch-off pressure.

In a variant of the invention, the control unit is structurally integrated into the pressure sensor and generates a shutdown signal for the engine control. Alternatively, however, it is also possible for the control unit to be structurally separate from the pressure sensor and for the pressure sensor to receive a pressure signal as an analog signal.

In the case of a consumer, it may be necessary for the pressure to be switched on again, for example, that there is a delay or a small leak occurs with a time lag or that the pressure can be reduced somewhat due to a strong cooling down. Such a Nachschaltdruck is typically 5-10% below the predetermined target value P _SOLL , but above the cut-off pressure P _OUT . In this case, only a very small flow rate may be fed into the system and needs further control, if not an excess amount of oil to be drained through the pressure relief valve. For this case, the duty cycle of the drive motor of the fluid pump ("pressure motor") is reduced so that only the speed is reached to achieve a lower pressure build-up by caster. This is done by reducing the constant K1 of the delivery volume Q and a proportionally reduced startup time of the pump motor drive.

The terms used in the invention of the input and. Turning Off the fluid pump preferably make sure that the drive of the fluid pump is fully switched on or off. However, the invention also claims protection for variants in which the drive of the fluid pump is merely raised or lowered.

In the preferred embodiment of the invention, the pressure medium system is a hydraulic system. However, the invention can also be implemented in other pressure medium systems, such as in pneumatic systems. All that is decisive is that the fluid pump after its shutdown still has a lag caused by inertia, during which the fluid pressure is still increasing.

It should also be mentioned that the pressure medium system according to the invention preferably comprises a consumer which is supplied with pressurized fluid. The consumer is preferably a clamping system for the mechanical clamping of workpieces or workpiece holders, such as workpiece pallets. Such clamping systems are known per se and, for example, in DE 31 36 177 A1 described, so that the content of this publication is fully attributable to the present specification. However, the invention also claims protection for fluid systems with other types of consumers.

Another aspect of the invention is concerned with the problem that the fluid pump at start-up (inertia) has an inertia-related flow, so that the fluid pressure during the flow of the fluid pump does not rise significantly, although the fluid pump is already turned on. The reasons for this flow are - as already briefly explained above - on the one hand in the dead time of the motor relay of the fluid pump and on the other in the delayed pressure build-up in the pressure fluid system.

Therefore, the invention preferably also provides that the control unit already switches the fluid pump back on when the fluid pressure drops in the switched-off state of the fluid pump, before the fluid pressure has fallen to a predetermined minimum pressure (eg 5% below target pressure), which should not be fallen below , The switch-on pressure (downstream pressure) of the fluid pump is thus preferably greater than the predetermined minimum pressure which should not be undershot. This offers the advantage that the possibly occurring further pressure drop during the inertia-related flow of the fluid pump does not lead to the predetermined minimum pressure being exceeded.

In a preferred embodiment of the invention detects the control unit in the off state of the fluid pump by means of a pressure sensor, the temporal change of the fluid pressure. The switch-on pressure is then by the control unit preferably in response to the time change of the fluid pressure in the off state of the fluid pump, the

mit:

k1, k2:

Konstanten, die den Druckverlauf während des Anlaufs der Fluidpumpe beim Nachschalten charakterisieren.

P_AUS:

Abschaltdruck, der unter Berücksichtigung des Nachlaufs beim Hochfahren des Drucks dazu führt, dass der Drucksollwert P_SOLL erreicht wird.

dP/dt:

Zeitliche Änderung des Fluiddrucks nach Erreichen des Maximalwertes. Die Steigung ist hierbei negativ, so dass der Nachschaltdruck P_EIN größer ist als der vorgegebene Minimaldruck P_MIN.

Cut-off pressure and the predetermined minimum pressure calculated, the calculation can be made according to the following formula: $${\mathrm{P}}_{\mathrm{ONE}}={\mathrm{P}}_{\mathrm{MIN}}-\left(\mathrm{k}\mathrm{1}+\mathrm{k}\mathrm{2}\cdot {\mathrm{P}}_{\mathrm{OUT}}\right)\cdot {\mathrm{dP}}_{\mathrm{IS}}/\mathrm{dt}$$

With:

k1, k2:

Constants that characterize the pressure curve during startup of the fluid pump when downstream.

P _OFF :

Cut-off, which leads taking into account the lag during start-up of the pressure to the desired pressure value P _SOLL is achieved.

dP / dt:

Time change of the fluid pressure after reaching the maximum value. The slope in this case is negative, so that the Nachschaltdruck P _ON is greater than the predetermined minimum pressure P _MIN.

The switch-on pressure (downstream pressure) is therefore preferably dimensioned such that the fluid pressure does not drop below the predetermined minimum pressure after the fluid pump has been switched on during the flow of the fluid pump.

It should also be mentioned that the invention also encompasses a corresponding operating method, as already evident from the above description.

Figur 1

eine schematische Darstellung eines erfindungsgemäßen Hydrauliksystems zur Hydraulikversorgung einer Spannvorrichtung.

Figur 2

das Betriebsverfahren des Hydrauliksystems aus Figur 1 in Form eines Flussdiagramms.

Figur 3A

den zeitlichen Verlauf des Hydraulikdrucks in dem Hydrauliksystem gemäß Figur 1.

Figur 3B

den zeitlichen Verlauf des Ein- bzw. Ausschaltzustands der Hydraulikpumpe.

Figur 3C

den zeitlichen Verlauf des Ein- bzw. Ausschaltzustands des Spannsystems.

Figur 3D

eine vergrößerte Darstellung des Druckverlaufs während des Nachlaufs der Hydraulikpumpe.

Figur 4

eine Abwandlung des Hydrauliksystems gemäß Figur 1, wobei die Steuereinheit in den Drucksensor integriert ist.

Figur 5A

den zeitlichen Verlauf des Hydraulikdrucks in einem herkömmlichen Hydrauliksystem.

Figur 5B

den zeitlichen Verlauf des Ein- bzw. Ausschaltzustands der Hydraulikpumpe in dem herkömmlichen Hydrauliksystem.

Figur 5C

den zeitlichen Verlauf des Ein- bzw. Ausschaltzustands des Spannsystems in dem herkömmlichen Hydrauliksystem.

Figur 5D

den zeitlichen Verlauf des Ein- bzw. Ausschaltzustands des Druckbegrenzungsventils in dem herkömmlichen Hydrauliksystem,

Figur 6

den zeitlichen Verlauf des Fluiddrucks in einem erfindungsgemäßen Druckmittelsystem, wobei der trägheitsbedingte Vorlauf der Hydraulikpumpe beim Nachschalten berücksichtigt wird, sowie

Figur 7

ein Flussdiagramm zur Verdeutlichung des Nachschaltens der Hydraulikpumpe zur Berücksichtigung des trägheitsbedingten Vorlaufs der Hydraulikpumpe.

Other advantageous developments of the invention are characterized in the subclaims or are explained in more detail below together with the description of the preferred embodiments of the invention with reference to FIGS. Show it:

FIG. 1

a schematic representation of a hydraulic system according to the invention for the hydraulic supply of a clamping device.

FIG. 2

the operating method of the hydraulic system of Figure 1 in the form of a flow chart.

FIG. 3A

the time course of the hydraulic pressure in the hydraulic system according to FIG. 1 ,

FIG. 3B

the time course of the on or off state of the hydraulic pump.

FIG. 3C

the time course of the on or off state of the clamping system.

Figure 3D

an enlarged view of the pressure curve during the wake of the hydraulic pump.

FIG. 4

a modification of the hydraulic system according to FIG. 1 , wherein the control unit is integrated in the pressure sensor.

FIG. 5A

the time course of the hydraulic pressure in a conventional hydraulic system.

FIG. 5B

the timing of the on or off state of the hydraulic pump in the conventional hydraulic system.

FIG. 5C

the timing of the on or off state of the clamping system in the conventional hydraulic system.

FIG. 5D

the timing of the on and off states of the pressure relief valve in the conventional hydraulic system,

FIG. 6

the time course of the fluid pressure in a pressure medium system according to the invention, wherein the inertia-related Flow of the hydraulic pump is considered when downstream, as well

FIG. 7

a flowchart for illustrating the subsequent switching of the hydraulic pump to take into account the inertia-related flow of the hydraulic pump.

FIG. 1 shows a hydraulic system according to the invention with a hydraulic pump 1, which is driven by an electric motor 2 and supplies a mechanical clamping system 3 with the hydraulic pressure required for operation.

The hydraulic pump 1 is connected on the input side to a hydraulic oil tank 4, from which the hydraulic pump 1 extracts hydraulic oil and pumps it via a check valve RV into a high-pressure region 5, to which the clamping system 3 is connected.

In addition, the hydraulic system has a pressure limiting valve 6, which connects the high-pressure region 5 with the hydraulic oil tank 4. The pressure limiting valve 6 is closed in the normal state and opens when the current hydraulic pressure P _IST in the high-pressure region 5 exceeds a predetermined maximum value P _MAX .

Furthermore, the hydraulic system has a pressure sensor 7, which measures the current hydraulic pressure P _IST in the high-pressure region 5 and forwards it to a control unit 8, which activates a motor control 9 as a function of the measured hydraulic pressure P _IST , the control unit 8 selectively switching on the electric motor 2 or turns off.

When controlling the electric motor 2, the control unit 8 also takes into account the current flow rate Q of the hydraulic pump 1, since the current flow rate Q influences the wake pressure increase. For this purpose, the control unit 8 with a Speed sensor 10 is connected, which detects the rotational speed n of the electric motor 2 and thus also the pump speed. From the pump speed n, the spreader unit 8 then calculates the current flow rate Q of the hydraulic pump 1.

In addition, a pressure reducing valve 11 is provided which branches off between the hydraulic pump 1 and the check valve RV and in the opened state recirculates hydraulic oil into the hydraulic oil tank 4, wherein the pressure reducing valve 11 is actuated by the control unit 8. The control unit 8 opens the pressure reducing valve 11 when the target value P _{SOLL is} lowered. This is useful so that the hydraulic pressure P _IST quickly drops to the new, lower target value P _SOLL.

mit:

P_AUS

Abschaltdruck.

P_SOLL:

Soll-Wert für den Fluiddruck.

K1:

Geräteabhängige Konstante, die die Trägheit von Fluidpumpe und Antriebsmotor wiedergibt.

K2:

Geräteabhängige Konstante, die Tot- und Verzögerungszeiten von Pumpe, Motor und Steuereinheit wiedergibt.

P_IST:

Aktueller Fluiddruck.

dP_IST/dt:

Zeitlicher Druckanstieg.

Q:

Förderstrom der Fluidpumpe.

The control unit 8 then calculates continuously during operation (see step S1 in FIG FIG. 2 ) a cut-off pressure P _OFF according to the following formula: $${\mathrm{P}}_{\mathrm{OUT}}={\mathrm{P}}_{\mathrm{SHOULD}}-\left(\mathrm{K}\mathrm{1}/{\mathrm{P}}_{\mathrm{SHOULD}}+\mathrm{K}\mathrm{2}\right)\cdot {\mathrm{dP}}_{\mathrm{IS}}/\mathrm{dt}\cdot \mathrm{1}/\mathrm{Q}$$

With:

P _OFF

Cut-off.

P _SOLL :

Target value for the fluid pressure.

K1:

Device-dependent constant representing the inertia of fluid pump and drive motor.

K2:

Device-dependent constant representing dead and delay times of pump, motor and control unit.

P _IST :

Current fluid pressure.

dP _/ dt:

Time pressure increase.

Q:

Flow of the fluid pump.

The device-specific constants K1, K2 can be determined beforehand in a calibration procedure.

When the hydraulic pump is switched off, the control unit 8 continuously measures the hydraulic pressure P _IST in the high-pressure area 5 by means of the pressure sensor 7 (compare step S2 in FIG FIG. 2 ).

The control unit 8 then continuously checks whether the measured hydraulic pressure P _{IST falls} below a predetermined switch-on pressure P _IN (compare S3 in FIG FIG. 2 ).

If so, the control unit 8 transmits a turn-on signal to the engine controller 9, which turns on the electric motor 2 to increase the hydraulic pressure P _IST (see step S4 in FIG FIG. 2 ).

In the subsequent pressure build-up, the control unit 8 then continuously checks whether the current hydraulic pressure P _IST exceeds the switch-off pressure P _OFF (compare step S5).

If this is the case, the control unit 8 sends a switch-off signal to the motor control 9, which subsequently shuts off the electric motor 2 (see step S6).

In the subsequent inertia-related overrun of the hydraulic pump 1, the hydraulic pressure P _{IST increases in} spite of the switched-off electric motor 2 due to inertia, wherein the caster pressure increase ΔP _NACHLAUF (see. Figure 3D ) Is sufficient to bridge the pressure difference AP between the cut-off pressure P _OFF and the predetermined target value P _SOLL. During the overrun, the hydraulic pressure P _IST thus rises from the switch-off pressure P _OUT to the setpoint value P _SOLL .

During the overrun, the pressure limiting valve 6 continuously checks whether the hydraulic pressure P _IST exceeds a predefined maximum value P _MAX (compare step S7 in FIG FIG. 2 ).

If this is the case, then the pressure relief valve 6 opens automatically and returns the excess hydraulic oil from the high-pressure area 5 into the hydraulic oil tank 4 in order to prevent a further pressure increase beyond the maximum value P _MAX (see step S8 in FIG FIG. 2 ).

In addition, the pressure limiting valve 6 continuously checks whether the hydraulic pressure P _{IST has} fallen below the predetermined desired value P _SOLL (compare step S9 in FIG FIG. 2 ).

If this is the case, the pressure relief valve 6 automatically closes in order to prevent further outflow of hydraulic oil from the high-pressure region 5 into the hydraulic oil tank 4, since the hydraulic pressure P _{IST would} thereby fall further below the predetermined desired value P _SOLL ( _FIG. see step S10 in FIG FIG. 2 ).

Out Figure 3D is also apparent that the maximum possible without a pressure limit caster pressure increase ΔP _{NACH-LAUF is} greater than the bridged pressure difference .DELTA.P between the cut-off pressure P _OFF and the predetermined target value P _SOLL . This is advantageous because the increase in pressure during the follow-up thereby relatively quickly. However, this advantage is achieved with the disadvantage that part of the hydraulic oil delivered during the overrun must be returned to the hydraulic oil tank 4 via the pressure limiting valve 6.

The embodiment according to FIG. 4 agrees further with the embodiment according to FIG. 1 to avoid repetition, reference is made to the above description, wherein like reference numerals are used for corresponding details.

A special feature of this embodiment is that the control unit 8 is arranged in a common housing 11 with the pressure sensor 7.

The FIGS. 6 and 7 illustrate an aspect of the invention, which is based on the problem of inertia-related timing of the hydraulic pump 1. Thus, the hydraulic pressure P _IST after switching on (aftershifting) of the hydraulic pump 1 at the time t _ON does not increase again immediately, since the pressure increase is delayed by the dead time of the motor relay of the hydraulic pump 1 and the pressure rise itself requires a certain lead time. The invention therefore provides, in this aspect, for the hydraulic pump 1 to be switched on again at a switch-on pressure P _ON , which is above the predetermined minimum pressure P _MIN , so that the predetermined minimum pressure P _{MIN is} not undershot despite the inertia-related flow of the hydraulic pump 1 ,

In a first step S1, device-specific constants K1, K2 are determined for this purpose, which characterize the pressure rise after switching on the hydraulic pump 1 during the flow of the hydraulic pump 1.

In a further step S2, the minimum pressure P _{MIN is} set, which should not be undershot.

In addition, in a step S3, the cut-off pressure P _{OUT is} calculated, which leads to a shutdown of the hydraulic pump 1 when the fluid pressure P _IST is raised. The calculation of the switch-off pressure P _OUT has already been explained in detail above, so that in this regard reference is made to the above statements to avoid repetition.

In a loop, the fluid pressure P _IST is first measured in a step S4.

Moreover, is then computed in the loop in a step S5, the time variation dP / dt _is the fluid pressure P _IST.

In a further step S6, the connection pressure P _ON is then calculated according to the following formula: $${\mathrm{P}}_{\mathrm{ONE}}={\mathrm{P}}_{\mathrm{MIN}}-\left(\mathrm{k}\mathrm{1}+\mathrm{k}\mathrm{2}\cdot {\mathrm{P}}_{\mathrm{OUT}}\right)\cdot {\mathrm{dP}}_{\mathrm{IS}}/\mathrm{dt}\mathrm{,}$$

In step S7 is then checked in the loop, whether the measured fluid pressure P _IST the calculated Anschaltdruck P _A drops below. If so, the hydraulic pump 1 is turned on in a step S8. Otherwise, the above-mentioned steps S4-S7 are repeated in a loop.

In this way, it is ensured that the fluid pressure P _IST does not fall below the predetermined minimum pressure P _MIN despite the inertia-related flow of the hydraulic pump 1, which should not be fallen below.

The subsequent switching in the proposed manner is advantageous because again the kinetic energy of the pump motor unit is utilized and no substantially higher pressure than the target pressure is established. Thus, with such a device, a pressure value can be set without too much oil volume was pumped through the pump, which must be removed via a limiting valve again.

In combination with the switching off of the pump according to the invention, even before the setpoint value P _SOLL is reached, a pressure _{adjustment system} results, in which the pressure limiting valve 6 only still serves security. The pressure setting is made by changing the setpoint value P _SOLL .

By using the cut-off pressure P _OFF from the initial pressure rise slightly more energy is added to the hydraulic system, as the pressure only in the system from the hydraulic pump 1 and the pressure pipe has to be established, and only after the opening of the check valve RV the entire hydraulic system is connected.

The invention is not limited to the preferred embodiments described above. Rather, a variety of variants and modifications are possible, which also make use of the concept of the invention and therefore fall within the scope. Moreover, the invention also claims protection for the subject matter and the features of the subclaims independently of the claims referred to.

LIST OF REFERENCE NUMBERS

1

hydraulic pump

2

electric motor

3

clamping system

4

Hydraulic oil tank

5

High pressure area

6

Pressure relief valve

7

pressure sensor

8th

control unit

9

motor control

10

Speed sensor

11

Pressure reducing valve

k1, k2

Constants that characterize the pressure curve during start-up of the fluid pump when downstream

K1

Device-dependent constant representing the inertia of fluid pump and drive motor

K2

Device-dependent constant representing dead and delay times of pump, motor and control unit

n

Speed of the electric motor

P _OFF

Cut-off

P _ON

Cut-in

P _IS

hydraulic pressure

P _MIN

Minimal

P _MAX

maximum pressure

P _SOLL

Target value

.DELTA.P

Pressure difference between cut-off pressure and setpoint value

ΔP _RUNNING

Trailing-pressure rise

RV

check valve

Q

Flow rate of the hydraulic pump

dP _ist / dt

temporal change of the hydraulic pressure

Claims (13)

1. A pressure means system, in particular a hydraulic system, with

   a) a fluid pump (1) for conveying a drive fluid with a certain discharge flow (Q) and a certain fluid pressure (P_IST),

   b) a control unit (8), which switches the fluid pump (1) on or off to adjust a predefined target value (P_SOLL) of the fluid pressure (P_IST),

   c) wherein the fluid pump (1) has an inertia-induced overrun during shut-off, so that the fluid pressure still rises during the overrun of the fluid pump (1), while the fluid pump (1) is already switched off,

   d) while the fluid pump (1) has an inertia-induced pre-run during switching-on, so that the fluid pressure does not yet substantially rises during the pre-run of the fluid pump (1), while the fluid pump (1) is already switched on,
   characterized in

   e) that the control unit (8) switches off the fluid pump (1) when increasing the fluid pressure (P_IST) to the predefined target value (P_SOLL) before the fluid pressure (P_IST) has reached the target value (P_SOLL), and/or

   f) that the control unit (8) switches on the fluid pump (1) again at the drop of fluid pressure (P_IST) when the fluid pump (1) is switched off before the fluid pressure (P_IST) has fallen to a predefined minimum pressure (P_MIN).
2. The pressure means system according to claim 1, characterized in that

   a) the fluid pressure (P_IST) still rises during the overrun after switching off of the fluid pump (1) without any pressure limitation by a certain maximum possible overrun pressure rise (ΔP_NACHLAUF), and

   b) the control unit (8) switches off the fluid pump (1) when the fluid pressure (P_IST) exceeds a certain switch-off pressure (P_AUS).
3. The pressure means system according to claim 2, characterized in that

   a) the pressure difference (ΔP) between the predefined target value (P_SOLL) of the fluid pressure (P_IST) and the switch-off pressure (P_AUS) is smaller than the maximum possible overrun pressure rise (ΔP_NACHLAUF), so that the fluid pressure (P_IST) during the overrun still rises at least up to the predefined target value (P_SOLL), and/or

   b) the maximum possible overrun pressure rise (ΔP_NACHLAUF) exceeds the pressure difference (ΔP) between the predefined target value (P_SOLL) of the fluid pressure (P_IST) and the switch-off pressure (P_AUS) by at least 10%, 20%, 50%, 100% or 200%, and/or

   c) the maximum possible overrun pressure rise (ΔP_NACHLAUF) exceeds the pressure difference (ΔP) between the predefined target value (P_SOLL) of the fluid pressure (P_IST) and the switch-off pressure (P_AUS) by at most 200%, 100%, 50%, 20% or 10%.
4. The pressure means system according to any one of the preceding claims, characterized in that

   a) a pressure sensor (7) is provided, which measures the fluid pressure (P_IST) and forwards the measured fluid pressure (P_IST) to the control unit (8), and

   b) the control unit (8) switches off the fluid pump (1) depending on the measured fluid pressure (P_IST) and/or

   c) the control unit (8) switches on the fluid pump (1) depending on the measured fluid pressure (P_IST) and/or

   d) the control unit (8) switches off the fluid pump (1) when the measured fluid pressure (P_IST) exceeds a certain switch-off pressure (P_AUS), and/or

   e) the control unit (8) switches on the fluid pump (1) when the measured fluid pressure (P_IST) falls below a certain switch-on pressure (P_EIN).
5. The pressure means system according to claim 4, characterized in that

   a) the control unit (8) determines the discharge flow (Q) of the fluid pump (1),

   b) the control unit (8) determines the switch-off pressure (P_AUS) depending on the discharge flow (Q) of the fluid pump (1) and the predefined target value (P_SOLL) of the fluid pressure (P_IST).
6. The pressure means system according to claim 5, characterized in that

   a) the fluid pump (1) is driven by a drive motor (2), in particular an electric drive motor (2), with a certain rotational speed, and

   b) the control unit (8) calculates the discharge flow of the fluid pump (1) from the rotational speed of the drive pump.
7. The pressure means system according to any one of the claims 4 to 6, characterized in that the control unit (8) adapts the switch-off pressure dynamically during operation, in particular depending on at least one of the following values:

   - the discharge flow (Q) of the fluid pump (1),

   - the predefined target value (P_SOLL) for the fluid pressure (P_IST),

   - the temporal pressure rise (dP/dt) of the fluid pressure (P_IST).
8. The pressure means system according to any one of the claims 3 to 7, characterized in that

   a) the fluid pump (1) is driven by a drive motor (2), in particular by an electric drive motor (2),

   b) the drive motor (2) is controlled by a motor control unit,

   c) the control unit (8) transmits a switch-off signal to the motor control unit for switching off the fluid pump (1).
9. The pressure means system according to claim 8, characterized in that

   a) the control unit (8) is constructionally integrated into the pressure sensor (7), or

   b) the control unit (8) is constructionally separate from the pressure sensor (7).
10. The pressure means system according to any one of the preceding claims, characterized in that

    a) the drive fluid is a hydraulic fluid, in particular a hydraulic oil, and that the fluid pump (1) is a hydraulic pump, and/or

    b) the fluid pump (1) supplies a consumer (3) with the drive fluid, and/or

    c) the consumer (3) is a mechanical clamping system (3), which clamps a workpiece or a workpiece holder detachably.
11. The pressure means system according to claim 4 and claim 10, characterized in that

    a) the control unit (8) determines the temporal change (dp/dt) of the fluid pressure (P_IST) when the fluid pump (1) is in the switched-off state, by means of the pressure sensor (7), and

    b) the control unit (8) determines the switch-on pressure (P_EIN) depending on at least one of the following values:

    - the temporal change (dP_IST/dt) of the fluid pressure (P_IST) when the fluid pump (1) is in the switched-off state,

    - the switch-off pressure (P_AUS),

    - the predefined minimum pressure (P_MIN).
12. The pressure means system according to claim 11, characterized in that

    a) the switch-on pressure (P_EIN) is greater than the predefined minimum pressure (P_MIN), and/or

    b) the switch-on pressure (P_EIN) is preferably dimensioned such that the fluid pressure (P_IST) after switching on the fluid pump (1) does not fall below the predefined minimum pressure (P_MIN) during the pre-run of the fluid pump (1).
13. An operating method for a pressure means system having

    a) a fluid pump (1) for conveying a drive fluid with a certain discharge flow (Q) and a certain fluid pressure (P_IST),

    b) a control unit (8), which switches the fluid pump (1) on or off to adjust a predefined target value (P_SOLL) of the fluid pressure (P_IST),

    c) wherein the fluid pump (1) has an inertia-induced overrun during shut-off, so that the fluid pressure still rises during the overrun of the fluid pump (1), while the fluid pump (1) is already switched off,

    d) while the fluid pump (1) has an inertia-induced pre-run during switching-on, so that the fluid pressure does not yet rise substantially during the pre-run of the fluid pump (1), although the fluid pump (1) is already switched on,
    characterized in

    e) that he control unit (8) switches off the fluid pump (1) when increasing the fluid pressure (P_IST) to the predefined target value (P_SOLL) before the fluid pressure (P_IST) has reached the target value (P_SOLL), and/or

    f) that the control unit (8) switches on the fluid pump (1) again at the drop of fluid pressure (P_IST) when the fluid pump (1) is switched off before the fluid pressure (P_IST) has fallen to a predefined minimum pressure (P_MIN).

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